U.S. patent application number 11/236683 was filed with the patent office on 2006-03-30 for mounting structure for an air-fuel ratio sensor in a motorcycle, and exhaust subassembly including same.
This patent application is currently assigned to Honda Motor Co., Ltd.. Invention is credited to Takeru Abe, Tomoya Kono, Mamoru Uraki, Ryutaro Yamazaki.
Application Number | 20060064964 11/236683 |
Document ID | / |
Family ID | 34937900 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060064964 |
Kind Code |
A1 |
Kono; Tomoya ; et
al. |
March 30, 2006 |
Mounting structure for an air-fuel ratio sensor in a motorcycle,
and exhaust subassembly including same
Abstract
A mounting structure is provided for an air-fuel ratio sensor on
an exhaust pipe in a motorcycle in which a concentration of oxygen
in an exhaust gas can be detected efficiently and accurately by the
air-fuel ratio sensor. The air-fuel ratio sensor is mounted on a
convergent connector of exhaust pipes, which, in turn, are
operatively connected to the cylinders of a multi-cylinder engine.
The air-fuel ratio sensor is located upstream of catalytic
converters provided in the exhaust pipes, and may be mounted so as
to be oriented substantially vertically when the motorcycle is in
an upright configuration, or alternatively, may be inclined toward
the rear of the motorcycle.
Inventors: |
Kono; Tomoya; (Saitama,
JP) ; Abe; Takeru; (Saitama, JP) ; Yamazaki;
Ryutaro; (Saitama, JP) ; Uraki; Mamoru;
(Saitama, JP) |
Correspondence
Address: |
CARRIER BLACKMAN AND ASSOCIATES
24101 NOVI ROAD
SUITE 100
NOVI
MI
48375
US
|
Assignee: |
Honda Motor Co., Ltd.
Tokyo
JP
|
Family ID: |
34937900 |
Appl. No.: |
11/236683 |
Filed: |
September 27, 2005 |
Current U.S.
Class: |
60/276 ;
60/323 |
Current CPC
Class: |
F01N 13/008 20130101;
B62J 99/00 20130101; F01N 13/009 20140601; B62J 45/40 20200201;
F02B 77/086 20130101; F01N 13/107 20130101; F01N 2560/025 20130101;
F02B 61/02 20130101; F01N 13/011 20140603 |
Class at
Publication: |
060/276 ;
060/323 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 7/10 20060101 F01N007/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2004 |
JP |
2004-286063 |
Claims
1. In a motorcycle of the type having a multi-cylinder engine and
an exhaust system comprising a separate exhaust pipe extending from
each respective cylinder of the engine, the improvement comprising
improved mounting structure in said exhaust system for supportively
receiving an air-fuel ratio sensor used for detecting the
concentration of oxygen in an exhaust gas of the motorcycle,
wherein the exhaust pipes are joined together at a convergent
connector, and wherein said air-fuel ratio sensor is mounted on the
convergent connector of said exhaust pipes connected to the
cylinders of said engine.
2. The mounting structure according to claim 1, wherein said
exhaust system comprises at least one catalytic converter
operatively connected to a plurality of said exhaust pipes, and
wherein said air-fuel ratio sensor is located upstream of said at
least one catalytic converter.
3. The mounting structure according to claim 2, wherein said
convergent connector comprises a connector body having an inclined
surface, and wherein the air-fuel ratio sensor is mounted on the
inclined surface of said convergent connector so as to be inclined
toward the rear of said motorcycle.
4. The mounting structure according to claim 1, wherein said
convergent connector comprises a connector body having an inclined
surface, and wherein the air-fuel ratio sensor is mounted on the
inclined surface of said convergent connector so as to be inclined
toward the rear of said motorcycle.
5. The mounting structure according to claim 1, wherein the
convergent connector comprises a tubular portion having a side wall
with a hole formed therein; wherein said mounting structure further
comprises a reinforcing member attached to the side wall of the
tubular portion, the reinforcing member comprising a cylindrical
collar with a threaded hole formed therein; and wherein the
air-fuel ratio sensor has an end cap with male threads thereon
which fit in the threaded hole of the cylindrical collar.
6. The mounting structure of claim 1, wherein said air-fuel ratio
sensor is mounted on the exhaust pipe so as to be pointed
substantially vertically upwardly when said motorcycle is oriented
in an upright configuration.
7. In a motorcycle of the type having a multi-cylinder engine and
an exhaust system comprising a separate exhaust pipe extending from
each respective cylinder of the engine, the improvement comprising
improved mounting structure in said exhaust system for supportively
receiving an air-fuel ratio sensor used for detecting the
concentration of oxygen in an exhaust gas of the motorcycle, the
improvement comprising a mounting structure formed in said exhaust
system for supportively receiving a plurality of air-fuel ratio
sensors, wherein selected exhaust pipes are joined together at
least two convergent connectors, and wherein an air-fuel ratio
sensor is mounted on each of said at least two convergent
connectors, respectively.
8. The mounting structure of claim 7, wherein the at least two
convergent connectors are operatively connected together downstream
of the air-fuel ratio sensors, so as to form a single common
convergent connector.
9. The mounting structure according to claim 7, wherein said
exhaust system comprises at least one catalytic converter
operatively connected to a plurality of said exhaust pipes, and
wherein said air-fuel ratio sensors are located upstream of said at
least one catalytic converter.
10. An exhaust subassembly for a motorcycle having a multi-cylinder
engine, said exhaust subassembly comprising a separate exhaust pipe
for placement extending from each respective cylinder of the
engine, wherein the exhaust pipes are joined together at a
convergent connector, said exhaust system comprising improved
mounting structure for supportively receiving an air-fuel ratio
sensor used for detecting the concentration of oxygen in an exhaust
gas of the motorcycle, and wherein said improved mounting structure
comprising a cylindrical collar provided on said convergent
connector and having threads formed therein; and an air-fuel ratio
sensor threadably attached to said cylindrical collar.
11. The exhaust subassembly of claim 10, further comprising at
least one catalytic converter operatively connected to a plurality
of said exhaust pipes, and wherein said air-fuel ratio sensor is
located upstream of said at least one catalytic converter.
12. The exhaust subassembly of claim 10, wherein said convergent
connector comprises a connector body having an inclined surface,
and wherein the air-fuel ratio sensor is mounted on the inclined
surface of said convergent connector so as to be inclined toward
the rear of said motorcycle in an installed configuration of said
subassembly.
13. The exhaust subassembly of claim 10, wherein the convergent
connector comprises a tubular portion having a side wall with a
hole formed therein; wherein said mounting structure further
comprises a reinforcing member attached to the side wall of the
tubular portion, the cylindrical collar forming a part of said
reinforcing member; and wherein the air-fuel ratio sensor has an
end cap with male threads thereon which fit in the threaded hole of
the cylindrical collar.
14. The exhaust subassembly of claim 10, wherein said air-fuel
ratio sensor is mounted on the exhaust pipe so as to be pointed
substantially vertically upwardly when said motorcycle is oriented
in an upright configuration.
15. The exhaust subassembly of claim 10, wherein the subassembly is
configured for use with a two-cylinder engine.
16. The exhaust subassembly of claim 10, wherein the subassembly is
configured for use with a four-cylinder engine.
17. The exhaust subassembly of claim 10, wherein the subassembly is
configured for use with a six-cylinder engine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention claims priority under 35 USC 119 based
on Japanese patent application No. 2004-286063, filed on Sep. 30,
2004. The subject matter of this priority document is incorporated
by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an air-fuel ratio sensor,
to a structure for mounting the sensor to an exhaust system
component of a motorcycle, and to an exhaust subassembly
incorporating the sensor. More particularly, the present invention
relates to a mounting structure for affixing an air-fuel ratio
sensor to an exhaust pipe in a motorcycle, and to a related exhaust
subassembly including the sensor, the mounting structure, and the
exhaust pipe.
[0004] 2. Background Art
[0005] It is well known to employ an oxygen sensor in a motorcycle
exhaust system, so as to improve the catalytic efficiency thereof.
In a motorcycle having a multi-cylinder engine, such an oxygen
sensor is typically mounted on a convergent connector of exhaust
pipes at a position upstream of a catalytic converter and spaced
apart from the engine on the rear lower side thereof. The catalytic
converter is used for exhaust purification, for example, and may
comprise a three-way catalyst. In a motorcycle having a
single-cylinder engine, such an oxygen sensor is located in an
empty space, the space selected such that the sensor does not
interfere with the engine body. This position improves the
maintainability of the sensor and protects the sensor.
[0006] Related to this mounting structure, there has been proposed
an invention entitled "Air-Fuel Ratio Control Device for Internal
Combustion Engine" (Japanese Laid-open Patent No. Sho 59-74360). In
Japanese Laid-open Patent No. Sho 59-74360, a catalyst for exhaust
purification is provided in an exhaust pipe of an internal
combustion engine for a vehicle, and an exhaust gas sensor is
mounted upstream of the catalyst. The composition of an exhaust gas
to be supplied to the catalyst is detected by the exhaust gas
sensor, and the air-fuel ratio for an air-fuel mixture to be taken
into the engine is controlled according to a detection signal
output from the exhaust gas sensor. According to the description in
Japanese Laid-open Patent No. Sho 59-74360, feedback control of
such an air-fuel ratio is performed by a known air-fuel ratio
control device, so that the composition of the exhaust gas is
optimized, allowing best purification of the exhaust gas by the
catalyst. Further, Japanese Laid-open Patent No. Sho 59-74360 also
discloses that an oxygen sensor for detecting the concentration of
oxygen in an exhaust gas is generally used as the exhaust gas
sensor.
[0007] Further, according to the description in an invention
entitled "Exhaust Gas Sensor Device in Motorcycle" (Japanese
Laid-open Patent No. 2000-335467), an exhaust gas sensor, for
detecting the concentration of oxygen or the like in an exhaust gas
discharged from an engine mounted on a motorcycle, may be mounted
on an upper wall of an exhaust pipe at a position on the front side
of a right projecting portion of a crankcase, and on the outer side
of a right side surface of a cylinder block.
[0008] In both of the references cited above, an oxygen sensor is
used as the exhaust gas sensor. This kind of oxygen sensor
determines whether the air-fuel ratio is rich or lean with respect
to a stoichiometric air-fuel ratio in a narrow region near the
stoichiometric air-fuel ratio, but it is not suitable for linear
detection of the oxygen concentration over a wide range of
values.
[0009] Also in a motorcycle, it is desirable to detect the air-fuel
ratio in a wide region by using an air-fuel ratio sensor in place
of the oxygen sensor mentioned above. In other words, the oxygen
sensor merely detects the presence or absence of oxygen in an
exhaust gas as mentioned above, whereas the air-fuel ratio sensor
can linearly detect the oxygen concentration in an exhaust gas over
a wide range by using an element whose output voltage changes in
proportion to the oxygen concentration. However, since the air-fuel
ratio sensor detects the oxygen concentration over a wide range
rather than in a narrow region near the stoichiometric air-fuel
ratio as mentioned above, the detection accuracy of the air-fuel
ratio sensor may be affected significantly by the location of the
air-fuel ratio sensor.
[0010] Accordingly, it is an object of the present invention to
provide a mounting structure for an air-fuel ratio sensor on a
motorcycle, wherein the concentration of oxygen or the like can be
efficiently and accurately detected by the air-fuel ratio
sensor.
SUMMARY OF THE INVENTION
[0011] According to a first aspect of the present invention, a
mounting structure is provided for an air-fuel ratio sensor in a
motorcycle having a multi-cylinder engine, where the sensor is used
for detecting the concentration of oxygen in the exhaust gas of the
motorcycle. In the structure according to the first aspect hereof,
the air-fuel ratio sensor is mounted on at least one of a plurality
of exhaust pipes connected to the cylinders of the engine.
[0012] With this arrangement, the concentration of oxygen in the
exhaust gas passing through the plural exhaust pipes can be
detected by a minimum number of air-fuel ratio sensors. Preferably,
the air-fuel ratio sensor is located upstream of one or more
catalytic converter(s) provided in the exhaust pipes, thereby
allowing control of the air-fuel ratio such that the combustion
efficiency can be improved, and the effectiveness of the catalytic
converters can be promoted. The air-fuel ratio sensor may be
mounted on an inclined surface of the convergent connector, so as
to be inclined towards the rear of the motorcycle. With this
arrangement, the amount of inward projection of the air-fuel ratio
sensor can be reduced, to thereby provide adequate space for the
flow of exhaust gas.
[0013] According to the present invention, the concentration of
oxygen in the exhaust gas can be efficiently and accurately
detected by using a necessary and sufficient number of air-fuel
ratio sensors in accordance with a number of variables, including
various types of engines, the number of cylinders, the number of
exhaust pipes, etc. Moreover, it is possible to perform air-fuel
ratio control, such that the effectiveness of the catalytic
converters can be promoted.
[0014] For a more complete understanding of the present invention,
the reader is referred to the following detailed description
section, which should be read in conjunction with the accompanying
drawings. Throughout the following drawings and description, like
numbers refer to like parts. The above-mentioned object, other
objects, characteristics and advantages of the present invention
will become apparent form the detailed description of the
embodiment of the invention presented below in conjunction with the
attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a simplified side plan view of a motorcycle having
a two-cylinder engine and including an air-fuel ratio sensor
mounted according to a first illustrative embodiment of the present
invention, where the air-fuel ratio sensor is mounted on a medial
connector joining two exhaust pipes.
[0016] FIG. 2 is a top plan view of the isolated exhaust system
which is a component of the motorcycle of FIG. 1, including a
sensor mounting structure according to the first illustrative
embodiment of the invention, showing the layout of the medial
connector and the air-fuel ratio sensor.
[0017] FIG. 3 is a vertical sectional view showing the air-fuel
ratio sensor shown in FIGS. 1-2, shown mounted substantially
vertically in an upper surface of an exhaust connector.
[0018] FIG. 4 is a perspective view of a motorcycle having a
four-cylinder engine and including an air-fuel ratio sensor
according to a second illustrative embodiment of the present
invention, where the air-fuel ratio sensor is mounted on a medial
connector for four exhaust pipes.
[0019] FIG. 5 is a top plan view showing the exhaust system of the
motorcycle of FIG. 4, showing the layout of the medial connector
and the air-fuel ratio sensor.
[0020] FIG. 6 is a schematic plan view showing a third illustrative
embodiment of the present invention wherein first and second
air-fuel ratio sensors are mounted on first and second upstream
connectors of four exhaust pipes in a four-cylinder engine,
respectively.
[0021] FIG. 7 is a schematic plan view of an exhaust system for a
horizontally opposed six-cylinder engine showing a fourth
illustrative embodiment of the present invention wherein a first
air-fuel ratio sensor is mounted on a first convergent connector of
three exhaust pipes connected to three cylinders of the
six-cylinder engine on one side thereof, and a second air-fuel
ratio sensor is mounted on a second convergent connector of three
exhaust pipes connected to the remaining three cylinders of the
engine on the other side thereof.
DETAILED DESCRIPTION OF THE INVENTION
[0022] A number of selected illustrative embodiments of the
mounting structure of the air-fuel ratio sensor in the motorcycle
according to the present invention will now be described in detail
with reference to FIGS. 1 to 7. These embodiments are intended to
illustrate, rather than to limit the invention. It should be
understood that only structures considered necessary for clarifying
the present invention are described herein. Other conventional
structures, and those of ancillary and auxiliary components of the
system, are assumed to be known and understood by those skilled in
the art.
[0023] FIG. 1 is a simplified side plan view of a motorcycle 10
having an air-fuel ratio sensor 50, according to a first
illustrative embodiment of the present invention, mounted on a
convergent connector located medially in the exhaust system, at a
junction between two exhaust pipes. The motorcycle 10 itself has a
known structure. More specifically, a front wheel 12 is supported
to a front fork 14. The front fork 14 is connected to a frame 16. A
rear wheel 18 is provided at a rear portion of the frame 16. A seat
20 is fixed to the frame 16 at a position above the rear wheel 18.
A fuel tank 22 is also fixed to the frame 16. A two-cylinder engine
30 is provided below the fuel tank 22. A first exhaust pipe 32a and
a second exhaust pipe 32b extend from the two cylinders of the
engine 30 toward the rear side of the vehicle, respectively.
[0024] FIG. 2 is a top plan view showing the structure of the first
and second exhaust pipes 32a and 32b, shown removed from the
motorcycle 10 for purposes of clarity. The first exhaust pipe 32a
includes an upstream pipe member 33a and a downstream pipe member
36a. Similarly, the second exhaust pipe 32b includes an upstream
pipe member 33b and a downstream pipe member 36b. The upstream pipe
members 33a and 33b extend from the two cylinders of the engine 30
and are joined to each other to form a convergent connector 34. The
convergent connector 34 is branched outwardly at its downstream
end, to form the downstream pipe members 36a and 36b. The
downstream pipe members 36a and 36b are provided with a first
catalytic converter 38a and a second catalytic converter 38b,
respectively. The first catalytic converter 38a is connected at its
downstream end to a first muffler 40a, and the second catalytic
converter 38b is connected at its downstream end to a second
muffler 40b. Each of the first and second catalytic converters 38a
and 38b includes a three-way catalyst (not shown).
[0025] As shown in FIGS. 2 and 3, an air-fuel ratio sensor 50 is
mounted on the convergent connector 34, at a substantially central
position on the connector in the longitudinal direction thereof.
The sensor 50 is oriented on the convergent connector 34 so as to
be pointed in a substantially vertical direction, which will
normally be perpendicular to a road surface (not shown) when the
motorcycle 10 is upright and/or traveling straight ahead. That is,
the air-fuel ratio sensor 50 is mounted to the convergent connector
34 so that a central axis thereof is pointed in a substantially
vertical orientation when the vehicle is upright.
[0026] During operation of the motorcycle, exhaust gas discharged
from the cylinders of the engine 30 is introduced into the upstream
pipe members 33a, 33b of the first and second exhaust pipes 32a,
32b, respectively. The exhaust gas passing through these upstream
pipe members 33a and 33b is introduced into the convergent
connector 34, and the concentration of oxygen in the exhaust gas is
detected by the air-fuel ratio sensor 50 mounted on the convergent
connector 34. The detected oxygen concentration is converted into
an electrical signal, which is in turn supplied to a control unit
(not shown) to provide feedback to, and assist the control unit in
regulating the air-fuel ratio in the engine 30.
[0027] The exhaust gas passing through the convergent connector 34
flows subsequently downstream, and is introduced into the first and
second catalytic converters 38a and 38b, which oxidize hydrocarbons
(HC) and carbon monoxide (CO), and reduce nitrogen oxides (NOx).
Thereafter, the treated exhaust gas is discharged through the
mufflers 40a and 40b, to the outside of the vehicle. Accordingly,
it is possible to control the air-fuel ratio so as to permit a high
combustion efficiency and a sufficient catalytic function in the
first and second catalytic converters 38a and 38b.
[0028] As shown in FIG. 3, which is a cross sectional view of the
convergent connector 34 at a position where the air-fuel ratio
sensor 50 is mounted, the convergent connector 34 has a tubular
center section formed with a nut 41 affixed thereto in a suitable
opening 42 formed in a side wall thereof to receive the nut. This
opening 42 may be threaded internally, if desired, to permit
removal and replacement of the nut 41. The nut 41 includes a
cylindrical collar 44 with a threaded sensor mounting hole 45
formed therein, as shown, for receiving and mounting the air-fuel
ratio sensor 50. The sensor mounting hole 45 has an axis inclined
substantially vertically, when the motorcycle is in an upright
orientation thereof. In an alternative equivalent structure, the
nut 41 may be replaced with a reinforced boss (not shown) which is
welded on to convergent connector 34, which is integral therewith,
and which has threads formed internally therein.
[0029] In this first illustrative embodiment, the air-fuel ratio
sensor 50 is mounted on the convergent connector 34 of the two
exhaust pipes 32a and 32b at a position downstream of the
two-cylinder engine 30 and upstream of the first and second
catalytic converters 38a and 38b. Accordingly, the required
installation space for the air-fuel ratio sensor 50 is not large.
Moreover, the air-fuel ratio can be controlled by a minimum number
of air-fuel ratio sensors, that is, by the single air-fuel ratio
sensor 50, irrespective of the number of cylinders. Further, since
the air-fuel ratio sensor 50 is located upstream of the first and
second catalytic converters 38a and 38b, an efficient air-fuel
ratio can be given to improve efficiency of the three-way
catalyst.
[0030] FIGS. 4 and 5 show a second illustrative embodiment of the
present invention. In FIGS. 4 and 5, the same reference numerals as
those shown in FIGS. 1 to 3 will be used to denote the same or
similar parts, and the detailed description thereof will be
omitted. The same applies to the other illustrative embodiments of
the present invention.
[0031] The second illustrative embodiment relates to a motorcycle
having a four-cylinder engine 51. A first exhaust pipe 52a is
connected to the first cylinder of the engine 51, and a second
exhaust pipe 52b is connected to the second cylinder of the engine
51. As seen best in FIG. 5, the first exhaust pipe 52a and the
second exhaust pipe 52b are connected through a first junction
member 56a to a first intermediate pipe 58a. Similarly, a third
exhaust pipe 52c is connected to the third cylinder of the engine
51, and a fourth exhaust pipe 52d is connected to the fourth
cylinder of the engine 51. The third exhaust pipe 52c and the
fourth exhaust pipe 52d are connected through a second junction
member 56b to a second intermediate pipe 58b.
[0032] The first intermediate pipe 58a and the second intermediate
pipe 58b are joined to each other at a central convergent connector
60. The central convergent connector 60 has a similar structure to
that of the convergent connector 34 according to the first
embodiment, as described herein and as shown in FIG. 3. The central
convergent connector 60 is branched at its downstream end, to form
a right down pipe 62a and a left down pipe 62b. The right down pipe
62a and the left down pipe 62b are connected, at their respective
downstream ends, to a first catalytic converter 38a and a second
catalytic converter 38b, respectively.
[0033] In FIGS. 4 and 5, reference numerals 64a and 64b denote
first and second mufflers, respectively.
[0034] In the second illustrative embodiment, an air-fuel ratio
sensor 50 is mounted on the central convergent connector 60. The
exhaust gas discharged from the first and second exhaust pipes 52a
and 52b passes through the first junction member 56a and the first
intermediate pipe 58a to reach the central convergent connector 60.
Similarly, the exhaust gas discharged from the third and fourth
exhaust pipes 52c and 52d passes through the second junction member
56b and the second intermediate pipe 58b to reach the central
convergent connector 60.
[0035] The concentration of oxygen in the exhaust gas is detected
by the air-fuel ratio sensor 50 mounted on the central convergent
connector 60. As in the first illustrative embodiment, the oxygen
concentration detected above is converted into an electrical signal
to control the air-fuel ratio in the four-cylinder engine 51.
[0036] Also in the second illustrative embodiment shown in FIGS. 4
and 5, the exhaust gas discharged from the four cylinders of the
engine 51 is detected by the single air-fuel ratio sensor 50 to
control the air-fuel ratio in the engine 51.
[0037] Thus, the air-fuel ratio sensor 50 is efficiently located
with respect to the four cylinders to thereby allow the air-fuel
ratio control with a minimum number of sensors. Furthermore, since
the air-fuel ratio sensor 50 is located upstream of the first and
second catalytic converters 38a and 38b, an efficient air-fuel
ratio can be provided to the three-way catalyst.
[0038] FIG. 6 shows a third illustrative embodiment of the present
invention. FIG. 6 is a schematic illustration of a modified layout
of exhaust pipes, catalytic converters, and air-fuel ratio sensors,
based on the general configuration shown in FIG. 5.
[0039] That is, the third illustrative embodiment shown in FIG. 6
is different from the second illustrative embodiment shown in FIG.
5, only in that the single air-fuel sensor of FIG. 5 is replaced by
a pair of air-fuel sensors. In the embodiment of FIG. 6, a first
air-fuel ratio sensor 70a is mounted on the first intermediate pipe
58a, and a second air-fuel ratio sensor 70b is mounted on the
second intermediate pipe 58b. Accordingly, the first air-fuel ratio
sensor 70a is used to detect the concentration of oxygen in the
exhaust gas passed through the first and second exhaust pipes 52a
and 52b, respectively, connected to the first and second cylinders
of a four-cylinder engine. Similarly, the second air-fuel ratio
sensor 70b is used to detect the concentration of oxygen in the
exhaust gas passed through the third and fourth exhaust pipes 52c
and 52d, respectively, connected to the third and fourth cylinders
of the four-cylinder engine.
[0040] According to this illustrative embodiment, the oxygen
concentration in the first and second exhaust pipes 52a and 52b can
be detected by the first air-fuel ratio sensor 70a, and the oxygen
concentration in the third and fourth exhaust pipes 52c and 52d can
be detected by the second air-fuel ratio sensor 70b. Accordingly,
the air-fuel ratio in each cylinder of the four-cylinder engine can
be controlled more accurately, and a problem condition, such as a
leaky injector, can be diagnosed and located more easily than it
could be with only a single air-fuel sensor.
[0041] FIG. 7 shows a fourth illustrative embodiment of the present
invention. In the illustrative embodiment depicted in FIG. 7, a
horizontally opposed six-cylinder engine 80 is used, and two
air-fuel ratio sensors 70a and 70b are provided to control the
air-fuel ratio in the engine 80.
[0042] As shown in FIG. 7, a first exhaust pipe 82a, a second
exhaust pipe 82b, and a third exhaust pipe 82c, on the left side of
the engine 80, are joined together at a first convergent connector
84a. Similarly, a fourth exhaust pipe 82d, a fifth exhaust pipe
82e, and a sixth exhaust pipe 82f, on the right side of the engine
80, are joined together at a second convergent connector 84b.
[0043] The first air-fuel ratio sensor 70a is mounted on the inner
inclined surface of the first convergent connector 84a so as to be
inclined upwardly and toward the rear of the vehicle. Similarly,
the second air-fuel ratio sensor 70b is mounted on the inner
inclined surface of the second convergent connector 84b so as to be
inclined upwardly and toward the rear of the vehicle. With this
arrangement, the concentration of oxygen in the exhaust gas passed
through the first, second, and third exhaust pipes 82a, 82b, and
82c can be detected by the first air-fuel ratio sensor 70a, mounted
on the first convergent connector 84a. The concentration of oxygen
in the exhaust gas passed through the fourth, fifth, and sixth
exhaust pipes 82d, 82e, and 82f can be detected by the second
air-fuel ratio sensor 70b, mounted on the second convergent
connector 84b.
[0044] Also in this illustrative embodiment, the concentration of
oxygen in the exhaust gas passed through a plurality of exhaust
pipes can be detected by a minimum number of air-fuel ratio
sensors. Particularly in the case of the horizontally opposed
six-cylinder engine 80, the concentration of oxygen in the exhaust
gas discharged from the first to third cylinders of the engine 80,
on one side thereof, can be detected by the single air-fuel ratio
sensor 70a, and the concentration of oxygen in the exhaust gas
discharged from the fourth to sixth cylinders of the engine 80, on
the other side thereof, can be detected by the second air-fuel
ratio sensor 70b. Thus, the oxygen concentrations in the exhaust
gases discharged from the cylinders on one side of the engine 80
and from the cylinders on the other side of the engine 80 can be
individually detected, thereby attaining higher-precision air-fuel
ratio control. Further, since the first and second air-fuel ratio
sensors 70a and 70b are mounted so as to be inclined upwardly and
toward the rear of the vehicle, the amount of inward projection of
each sensor can be reduced.
[0045] As apparent from the above-mentioned illustrative
embodiments, the present invention is applicable to various types
of multi-cylinder engines such as a straight engine, a horizontally
opposed engine, and a V-engine.
[0046] While a working example of the present invention has been
described above, the present invention is not limited to the
working example described above, but various design alterations may
be carried out without departing from the present invention as set
forth in the claims.
* * * * *